Happy Holidays!

We wish you, your families, and your Elves all the best this holiday season! Let’s build something clever in 2017!


Build & Win An ELF at VCF Midwest

Celebrate the 40th anniversary of the COSMAC ELF computer by participating in a build of one at the Vintage Computer Festival Midwest --- and possibly taking it home with you! The idea is simple: drop by our booth at the festival and wire-wrap a connection or two (we’ll have the parts and tools and will show you how). Everyone who participates will get a raffle ticket, and the newly built ELF will then be raffled off. Bring your favorite kid along and give them a taste of microcomputing’s early days.

The design and build is very similar to the original ELF, but with a few improvements to lower its power requirements and provide for easy expansion. The design is primarily the work of Lee Hart (creator of the tiny, popular Membership Card computers) and Josh Bensadon, with parts donated by several community members.

The COSMAC ELF Turns 40

Illustration of a COSMAC ELF computer with a golden number "40" above it.

In August of 1976 the cover of Popular Electronics featured a peculiar little device built on a piece of perfboard with a 2-digit hexadecimal display, an LED, 11 toggle switches and a pushbutton. The text read “THE COSMAC ‘ELF’ --- A MICROCOMPUTER TRAINER THAT’S POWERFUL, EXPANDABLE AND COSTS AS LITTLE AS $80.” The large chip in the center of the perfboard was RCA’s CDP1802 COSMAC microprocessor.

The chip’s inventor and by far its greatest evangelist was Joseph Weisbecker, who wrote the article to introduce the hobbyist community to this simple CMOS microprocessor. The machine featured in the article was minimal: 256 bytes of RAM (less characters than two tweets on Twitter!) and no ROM. Yet the machine could be programmed, opcode by opcode, to play simple games, play music (if one wired up a speaker), or expanded to control external devices. For many, this hand-wired, low-cost machine was their first computer, and an entry into the world of microcomputing. There seems little doubt it helped launch more than a few engineering careers.

In Weisbecker’s view, everyone could eventually own and perhaps even understand and program their own personal computer, for productivity and entertainment. While he’d write future articles that expanded the ELF with such things as video and a photocell “light pen,” the beginning was about as simple as a computer could be.

40 years later, this is still a great little machine to build, play with, and learn on. Drop by the Vintage Computer Festival Midwest on September 10-11 to celebrate the anniversary with us!

Browse our Gallery to find builds of the original COSMAC ELF as well as the many creative home-built machines inspired by it.

System 00 Manual Now Online

Thanks to the Hagley Museum and Library, we now have the manual online for Weisbecker’s earliest known microprocessor prototype, System 00, available on the Publications > Books & Papers page. (We recently published photos of System 00 in the Gallery.)

System 00 dates back to about 1971 and was built with standard 7400-series TTL chips. The manual documents system architecture, opcodes, machine operation, and even includes schematics and sample programs. Let me know if you build one!

Get to Know FRED

In 1971, RCA engineer Joseph Weisbecker was prototyping his ideas for an 8-bit microprocessor. In August 1976, he published plans for a low-cost CDP1802-based computer in Popular Electronics, the COSMAC ELF. In between, Weisbecker developed and evangelized a concept he called FRED, for “Flexible Recreational and Educational Device.”

COSMAC ELF forum member Paul Robson contacted the Hagley Museum and Library about some archived FRED-related documents and, with their blessing, has made them available in the Files area of the COSMAC ELF forum (Yahoo account needed for access). The documents currently posted contain everything from prototype schematics to hand-coded software to random notes and doodles. They offer a rare and interesting peek into the minds of the engineers from the early days of microcomputing.

Birth of a Microprocessor


Photo by Z. Stachniak, courtesy of the David Sarnoff Library

Next month marks 40 years since Joseph Weisbecker published plans for the original ELF computer in the pages of Popular Electronics, but 5 years earlier Weisbecker was prototyping his ideas for a microprocessor out of discrete logic. Later Weisbecker would conceptualize his ideas for an inexpensive home computer as FRED (“Flexible Recreational and Educational Device”), eventually leading to RCA’s COSMAC series of microprocessors and the RCA VIP computer.

Thanks to Z. Stachniak and the David Sarnoff Library, we now have photographs of Weisbecker's prototype in the Gallery.

In completely unrelated news, today is Ringo Starr’s 76th birthday. Peace and love, everyone. :)

Vintage Computer Festival East 2016

Just a quick reminder that the Vintage Computer Festival East is coming up April 15-17 in Wall, New Jersey. Besides exhibits there are technical presentations, talks, and even a game programming hack-a-thon. Spot any COSMAC stuff? Send us photos!

Happy Holidays!

Wishing you, your family, and your Elves all the best for this holiday season. You don’t need more than 8 bits to be happy!


SPA-Tronics Classic Computer Show

The South-Pittsburgh Area Electronics Club Classic Computer Show is coming up in less than two weeks, with numerous computers from bygone days on exhibit. According to the group’s website and a recent forum post, you can expect to see COSMAC ELF class computers as well as an early Apple MacIntosh, a KIM-1, Sinclair computers, machines from Commodore and Radio Shack and more.

If you attend and would like to share any COSMAC related photos on, please let me know!

VCFMW 10.0 Photos

Josh Bensadon has published photos from the Vintage Computer Festival Midwest 10.0, held on August 29 and 30, 2015. Josh attended with Lee Hart to contribute some COSMAC fun to the event. Photos from other attendees may be found from links on’s Past Events page.

© Dave Ruske 2001-2017, except where noted